Hello, what kind of restriction are you thinking of? You mean because of the clamping power? I would say it should work. The best would be to ask Marton directly.
I have a 8.5" custom bar from him and tried it with two Zion Bikes stems. With one it was not clamping well, with the other one I have no problem at all. So tolerances may play a role here. The diameter of the clamping area of my bar is pretty much like for all other bars I have, so Marton provides good measurements here. In my case I am almost sure the tolerance issue was on the stem's side.